Method for adjusting a drive signal

ABSTRACT

A method for adjusting a drive signal of a drive circuit. A period of the drive signal is determined and an advance angle count value is extracted from a storage register in accordance with the period of the drive signal. The advance angle count value and a first control signal are used to determine an advance angle adjustment range, where the first control signal is from a source external to the drive circuit. The advance angle adjustment range and a second control signal are used to determine an advance angle adjustment range start angle, where the second control signal is from a source external to the drive circuit.

The present application is a continuation application of U.S. patentapplication Ser. No. 15/495,587 filed on Apr. 24, 2017, by TakashiOgawa, titled “MOTOR CONTROL CIRCUIT AND METHOD” which is a divisionalapplication of U.S. patent application Ser. No. 14/578,433 filed on Dec.20, 2014, now U.S. Pat. No. 9,667,176, by Takashi Ogawa, titled “MOTORCONTROL CIRCUIT AND METHOD” which is a nonprovisional application ofU.S. Provisional Patent Application No. 61/918,693, filed on Dec. 20,2013, which applications are hereby incorporated by reference in theirentirety, and priority thereto for common subject matter is herebyclaimed.

BACKGROUND

The present invention relates, in general, to motors and, moreparticularly, to three phase motors.

Multi-phase motors are used in a variety of applications including discdrives, digital video disc players, scanners, printers, plotters,actuators used in automotive and aviation industries, etc. Generally,multiple phase motors include a stationary portion or stator thatproduces a rotating magnetic field and a non-stationary portion or rotorin which torque is created by the rotating magnetic field. The torquecauses the rotor to rotate which in turn causes a shaft connected to therotor to rotate. The motors are driven by motor drive circuits.

Motor drive circuits are designed to meet desired motor performanceparameters which may include noise level specifications, start-upspecifications, maximum rotational speed specifications, etc. Noisespecifications may be set to provide continuity of current flow duringmotor startup, or during motor rotation, or during motor stoppage.Start-up or motive power specifications may be set so that the motorreliably starts. Rotational speed specifications may be set to ensurethere is sufficient torque drive to cover a large number of differentmotors. For example, the desired rotational speed of a server is higherthan that of a personal computer. It is commonly believed thatthree-phase motors are better at achieving the desired specificationscompared to single phase motors; however, three-phase motors cost morethan single phase motors. In addition, three-phase motors providecurrent having sinusoidal characteristics from motor start-up to motorstoppage or cessation and they allow accurate determination of motorposition and rotation speed. Three-phase motors typically include threeHall sensors, which is one of the reasons these motors are moreexpensive to manufacture. A Hall sensor may be referred to as a Hallelement. U.S. Pat. No. 6,359,406 issued to Hsien-Lin Chiu et al. on Mar.19, 2002, discloses three-phase motors and in particular discloses athree-phase motor having two Hall sensors or two Hall elements. Adrawback with this technology is that it uses special bias circuitrythat complicates its design and increases costs. A technique to lowerthe cost of three-phase motors is to manufacture the motor drivecircuitry as a sensorless motor drive circuit, i.e., a motor withoutsensors. U.S. Pat. No. 6,570,351 issued to Shinichi Miyazaki et al. onMay 27, 2003, discloses a three-phase motor without sensors. A drawbackwith sensor-less motor drive configurations is that they may fail tostart if the inductive voltage of the coil is small. Another drawbackwith this circuitry is that the lead angles are not optimized fordifferent applications.

Accordingly, it would be advantageous to have a multi-phase motor drivecircuit and a method for driving the motor that is suitable forproviding lead angles for different motors. It is desirable for themulti-phase drive circuit and method to be cost and time efficient toimplement.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from a reading of thefollowing detailed description, taken in conjunction with theaccompanying drawing figures, in which like reference charactersdesignate like elements and in which:

FIG. 1 is a diagrammatic representation of a motor that is driven by adrive circuit in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram further illustrating the drive circuit of FIG.1;

FIG. 3 is a circuit diagram of a lead angle adjustment circuit inaccordance with an embodiment of the present invention;

FIG. 4 is a flow diagram illustrating advance angle determination inaccordance with an embodiment of the present invention;

FIG. 5 is flow diagram showing the advance angle calculation process inaccordance with an embodiment of the present invention;

FIG. 6 is a circuit diagram illustrating a circuit configuration inwhich pins of a lead angle adjustment circuit are coupled for receivinga ground signal in accordance with an embodiment of the presentinvention;

FIG. 7 is a circuit diagram illustrating a circuit configuration inwhich pins of a lead angle adjustment circuit are coupled to voltagedivider networks in accordance with an embodiment of the presentinvention;

FIG. 8 illustrates a plot suitable for use in setting an advance anglein accordance with an embodiment of the present invention;

FIG. 9 illustrates a plot suitable for use in setting an advance anglein accordance with an embodiment of the present invention;

FIG. 10 is a plot illustrating a portion of a method for driving a motorin accordance with an embodiment of the present invention; and

FIG. 11 is a plot illustrating an improvement in the drive current inaccordance with an embodiment of the present invention.

For simplicity and clarity of illustration, elements in the figures arenot necessarily to scale, and the same reference characters in differentfigures denote the same elements. Additionally, descriptions and detailsof well-known steps and elements are omitted for simplicity of thedescription. As used herein current carrying electrode means an elementof a device that carries current through the device such as a source ora drain of an MOS transistor or an emitter or a collector of a bipolartransistor or a cathode or an anode of a diode, and a control electrodemeans an element of the device that controls current flow through thedevice such as a gate of an MOS transistor or a base of a bipolartransistor. Although the devices are explained herein as certainn-channel or p-channel devices, or certain n-type or p-type dopedregions, a person of ordinary skill in the art will appreciate thatcomplementary devices are also possible in accordance with embodimentsof the present invention. It will be appreciated by those skilled in theart that the words during, while, and when as used herein are not exactterms that mean an action takes place instantly upon an initiatingaction but that there may be some small but reasonable delay, such as apropagation delay, between the reaction that is initiated by the initialaction and the initial action. The use of the words approximately,about, or substantially means that a value of an element has a parameterthat is expected to be very close to a stated value or position.However, as is well known in the art there are always minor variancesthat prevent the values or positions from being exactly as stated. It iswell established in the art that variances of up to about ten percent(10%) (and up to twenty percent (20%) for semiconductor dopingconcentrations) are regarded as reasonable variances from the ideal goalof exactly as described.

It should be noted that a logic zero voltage level (V_(L)) is alsoreferred to as a logic low voltage or logic low voltage level and thatthe voltage level of a logic zero voltage is a function of the powersupply voltage and the type of logic family. For example, in aComplementary Metal Oxide Semiconductor (CMOS) logic family a logic zerovoltage may be thirty percent of the power supply voltage level. In afive volt Transistor-Transistor Logic (TTL) system a logic zero voltagelevel may be about 0.8 volts, whereas for a five volt CMOS system, thelogic zero voltage level may be about 1.5 volts. A logic one voltagelevel (V_(H)) is also referred to as a logic high voltage level, a logichigh voltage, or a logic one voltage and, like the logic zero voltagelevel, the logic high voltage level also may be a function of the powersupply and the type of logic family. For example, in a CMOS system alogic one voltage may be about seventy percent of the power supplyvoltage level. In a five volt TTL system a logic one voltage may beabout 2.4 volts, whereas for a five volt CMOS system, the logic onevoltage may be about 3.5 volts.

DETAILED DESCRIPTION

The present description includes, among other features, a motor drivecircuit and a method for driving a motor that includes adjusting a leadangle of a position indicator signal. The position indicator signal maybe referred to as an FG signal or a Hall sensor comparison signal. Acontrol circuit controls logic processing functions to adjust theappropriate amount of a lead at angle at any speed using two externalpins. A pseudo FG signal is generated in response to the voltagesapplied to the two external pins, wherein the pseudo FG signal has alead angle that can be optimized at any speed by adjusting one externalpin for fast motor speeds and adjusting the other external pin for slowmotor speeds. It should be noted that lead angle control may not beperformed during start up, but after the motor has gone through a numberof rotations.

Default values of the advance angle can be set by setting the externalpins to a source of operating potential, e.g., V_(SS) or V_(DD), using apull down resistor or a pull up resistor.

In accordance with an embodiment, a motor having a stator, a rotor, aplurality of coils coupled to the stator, and at least one Hall sensorcoupled to the stator is provided. A position indicator signal isgenerated in response to a signal from the at least one Hall sensor,wherein the position indicator signal has a first period. A phase shiftvalue using the position indicator signal is generated. Then, theposition indicator signal is adjusted to generate an adjusted positionindicator signal in response to the phase shift value.

In accordance with an aspect, generating the adjusted position indicatorsignal includes determining a number of times the position indicatorsignal transitions from a first level to a second level before adifference between a first edge of the position indicator signal and acorresponding first edge of the adjusted position indicator signalstabilize to form a first count value. Then, the first count value ismultiplied with a predetermined number to generate a multiplied countvalue. The multiplied count value is used to determine an amount toadvance the position indicator signal to form the adjusted positionindicator signal. In accordance with another aspect, a count adjustmentvalue is selected from a count adjustment value storage register. Thecount adjustment value and a first control signal coupled to a firstexternal pin are used to determine a slope of a first count adjustmentparameter. The first count adjustment parameter and a second controlsignal from a second external pin are used to determine a second countadjustment parameter.

In accordance with another aspect, the second count adjustment value iscombined with an advance angle control signal to generate a correctionfactor.

In accordance with another aspect, using the multiplied count value todetermine an amount to advance the adjusted position indicator signalincludes combining the multiplied count value with the correction factorto generate the adjusted position indicator signal.

In accordance with another aspect, the advance angle signal is generatedby determining a number of times the position indicator signaltransitions from the first level to the second level and generating astart signal in response to the number of times the position indicatorsignal transitions from the first level to the second level.

In accordance with another embodiment, a method for adjusting a drivesignal for a motor, comprises providing a drive circuit having a firstpin and a second pin, wherein the drive circuit generates the drivesignal and determining a period of the drive signal. An advance anglecount value is extracted from a storage register in accordance with theperiod of the drive signal and the advance angle count value and a firstcontrol signal coupled to the first input pin are used to determine anadvance angle adjustment range wherein the first control signal is froma source external to the drive circuit. The advance angle adjustmentrange and a second control signal coupled to the second input pin areused to determine an advance angle adjustment range start angle whereinthe second control signal is from a source external to the drivecircuit.

In accordance with another aspect, a first advance angle and a secondadvance angle are determined.

In accordance with another aspect, the first advance angle is a minimumadvance angle and the second advance angle is a maximum advance angle.

In accordance with another aspect, an angle determination slope isdetermined using the first advance angle and the second advance angle.

In accordance with another embodiment, a driver circuit includes a leadangle adjustment circuit, wherein the lead angle adjustment circuitcomprises a first counter having an input and an output and a multipliercircuit having an input and an output. The input of the multipliercircuit is coupled to the output of the first counter. A subtractorcircuit having a first input, a second input is coupled to the output ofthe multiplier circuit. A storage register having an input and an outputis coupled to the output of the first counter. A slope determinationcircuit having a first input, a second input and an output is coupled tothe output of the register, wherein the second input of the slopedetermination circuit is coupled to a first external pin of the leadangle adjustment circuit. A multiplier circuit having a first input, asecond input, and an output is coupled to the second input of the slopedetermination circuit. An input of the multiplier circuit is coupled toan external pin. An addition circuit having an input and an output iscoupled to the first summer.

FIG. 1 is a diagrammatic representation of a three-phase motor 10 thatis driven by a drive circuit 12 in response to one or more signals froma Hall sensor 14 in accordance with an embodiment of the presentinvention. Drive circuit 12 may be referred to as a driver and Hallsensor 14 may be referred to as a Hall element. Three-phase motor 10includes a stator 16 and a rotor 18 having a portion 20 magnetized witha first pole and a portion 22 magnetized with a second pole. By way ofexample, portion 20 is a north pole and portion 22 is a south pole. Acoil 24 is coupled to or mounted on a portion of stator 16, a coil 26 iscoupled to or mounted on another portion of stator 16, and a coil 28 iscoupled to or mounted on yet another portion of stator 16. Drive circuit12 is coupled to Hall sensor 14 via an electrical interconnect 29, tocoil 24 via an electrical interconnect 30, to coil 26 via an electricalinterconnect 32, and to coil 28 through an electrical interconnect 32.Coil 24 may be referred to as a U-phase winding, coil 26 may be referredto as a W-phase winding, and coil 28 may be referred to as a V-phasewinding. Electrical interconnects 30, 32, and 34 may be wires,electrically conductive traces, or the like.

FIG. 2 is a block diagram 50 further illustrating drive circuit 12. Itshould be noted that block diagram 50 includes diagrammaticrepresentations of drive circuit 12, three-phase motor 10, and Hallsensor 14. Drive circuit 12 includes an FG signal masking circuit 52, arotational state generation circuit 54, a pulse width modulation (“PWM”)detection circuit 56, a timer 58, a status controller 60, a duty controlcontroller 62, an output duty generation circuit 64, a drive controlsignal generation circuit 66, and an output drive stage 68. Moreparticularly, FG signal masking circuit 52 may be comprised of an FGsignal edge detector 70, a counter 72, and an FG signal judgment circuit74. FG signal edge detector 70 has an input that serves as an input 76of drive circuit 12, an output connected to an input of counter 72 andan output connected to an input of FG signal judgment circuit 74. Anoutput 78 of FG signal judgment circuit 74 serves as an output of FGsignal masking circuit 52. FG signal masking circuit 52 may be referredto as a chattering mitigation circuit or a chattering mitigationfeature.

Rotational state generation circuit 54 has inputs 80 and 82, aninput/output 84, and may be referred to as an FG generation circuit.Output 78 of FG signal masking circuit 52 is connected to input 80 of FGgeneration circuit 54. Input/output 84 may be referred to as aninput/output node, an I/O node, an input/output terminal, an I/Oterminal, or the like. Rotational state generation circuit 54 may becomprised of a control circuit 86 coupled to a multiplier circuit 88. Itshould be noted that input 80 and input 84 are connected to multipliercontrol circuit 86 and input/output 84 is connected to multipliercircuit 88. PWM detection circuit 56 has an output connected to an inputof state controller 60 and to an input of duty control controller 62 andis configured to determine the speed of rotor 18. It should be notedthat if the duty range is small the speed of the rotor is smaller thanif the duty range is large. Timer 58 has an output connected to input 82of rotational state generation circuit 54 and to an input 92 of statecontroller 60 and may include a timer counter 90. In addition, statecontroller 60 has an input/output 94 connected to an input/output 84 ofrotational state generation circuit 54, an input 98 connected to output78 of FG signal masking circuit 52, and an input/output 96 connected toan input/output 100 of duty control controller 62. By way of example,duty control controller 62 is comprised of a calculation device 102configured to determine an amount of change to the duty cycle, a summer104, and a PWM converter 106. Calculation device 102 has an input thatserves as input/output 100 and an output connected to an input of summer104. In addition, summer 104 has an output that is connected to an inputof PWM output converter 106 and to another input of summer 104. Anoutput 108 of PWM output converter 106 serves as an output of dutycontrol controller 62. State controller 60 is configured for determiningthe status or condition of the FG signal and the PWM signal and dutycontrol controller 62 is configured to control an output sine wave,which helps to make the motor quieter.

Output duty generation circuit 64 has an input 110 connected to anoutput 99 of output of state controller 60, an input 112 connected tooutput 108 of output duty generation circuit 62, and a plurality ofoutputs 114, 116, and 118 connected to corresponding inputs of drivecontrol signal generation circuit 66, which signal generation circuit 66has a plurality of outputs 120, 122, and 124 connected to correspondinginputs of output drive stage 68. In accordance with an embodiment, drivestage 68 includes driver devices 126, 128, and 130 having inputs thatserve as inputs 126A, 128A, and 130A of output drive stage 68, a pair66A of transistors having a terminal connected to U-phase winding 24, apair 66B of transistors having a terminal connected to W-phase winding26, and a pair 66C of transistors having a terminal connected to V-phasewinding 28. Pair of transistors 66A is comprised of transistors 66A₁ and66A₂, wherein each transistor has a control electrode, and a pair ofcurrent carrying electrodes. The control electrodes of transistors 66A₁and 66A₂ are coupled for receiving control signals from driver device126, one current carrying electrode of transistor 66A₁ is coupled forreceiving a source of potential V_(DD) and the other current carryingelectrode of transistor 66A₁ is connected to a current carryingelectrode of transistor 66A₂. The other current carrying terminal oftransistor 66A₂ is coupled for receiving a source of potential V_(SS)such as, for example, a ground potential. The commonly connected currentcarrying electrodes of transistors 66A₁ and 66A₂ are connected toU-phase winding 24.

Pair of transistors 66B is comprised of transistors 66B₁ and 66B₂,wherein each transistor has a control electrode, and a pair of currentcarrying electrodes. The control electrodes of transistors 66B₁ and 66B₂are coupled for receiving control signals from driver device 128, onecurrent carrying electrode of transistor 66B₁ is coupled for receiving asource of potential V_(DD) and the other current carrying electrode oftransistor 66B₁ is connected to a current carrying electrode oftransistor 66B₂. The other current carrying terminal of transistor 66B₂is coupled for receiving a source of operating potential V_(SS) such as,for example, a ground potential. The commonly connected current carryingelectrodes of transistors 66B₁ and 66B₂ are connected to U-phase winding26.

Pair of transistors 66C is comprised of transistors 66C₁ and 66C₂,wherein each transistor has a control electrode, and a pair of currentcarrying electrodes. The control electrodes of transistors 66C₁ and 66C₂are coupled for receiving control signals from driver device 130, onecurrent carrying electrode of transistor 66C₁ is coupled for receiving asource of potential V_(DD) and the other current carrying electrode oftransistor 66C₁ is connected to a current carrying electrode oftransistor 66C₂. The other current carrying terminal of transistor 66C₂is coupled for receiving a source of operating potential V_(SS) such as,for example, a ground potential. The commonly connected current carryingelectrodes of transistors 66C₁ and 66C₂ are connected to U-phase winding28.

A comparator 136 has inputs connected to corresponding inputs of a Hallsensor 14 and an output 138 connected to input 76 of rotational stategeneration circuit 54.

It should be noted that in accordance with an alternative embodiment, FGsignal masking circuit 52 is absent from drive circuit 12 and thatoutput 138 of comparator 136 is commonly connected to input 76 ofrotational state generation circuit 54 and to input 98 of statecontroller 60.

In accordance with another embodiment of the present invention, theefficiency of the rotation of a rotor of a motor is improved byadjusting the lead angle of the drive signal. It should be noted thatthe lead angle may also be referred to as an advance angle. By way ofexample, a drive circuit such as drive circuit 12 may be configured tohave two external pins to which a pseudo-FG signal may be applied tocontrol the lead angle of the drive signal. A Hall sensor, such as Hallsensor 14, provides data regarding the rotational speed of the rotor.One external pin may be used in response to the rotor operating at aslower speed and the other external pin may be used in response to therotor operating at a higher speed. The advance angle may be determinedby applying a voltage to one pin for a rotor operating at low speed andapplying a voltage at the other pin for a rotor operating at a highspeed. An operating point that includes the desired advance angle can bedetermined using a linear analysis between the low speed operation andthe high speed operation. The advance angle may be increased at a fixedrate.

In accordance with an embodiment, an advance angle value is determinedbased on data for rotation speed obtained from a single Hall sensor. Thevalue of the advance angle is determined by strait line approximationrunning between a point during low-speed rotation and a point duringhigh-speed rotation. The point used for both low-speed rotation andhigh-speed rotation may be changed by using external pins.

The advance angle control is useful after rotation has been initiated.The advance angle value is increased at a fixed rate determined by thestrait line approximation based on an increase of rotation speed.Because two points are used for the strait-line approximation fordetermining an advance angle value, less data is used and it is able towork efficiently without enlarging circuit size.

FIG. 3 is a circuit diagram of a lead angle adjustment circuit 200 inaccordance with an embodiment of the present invention. What is shown inFIG. 3 is an FG period counter 202, a multiplier circuit 204, an advanceangle storage register 206, an advance angle range calculation circuit208, an advance angle slope counter circuit 210, an advance angleinitial addition calculation circuit 212, an addition circuit 214, asubtractor circuit 216, a Pseudo-FG generation circuit 218, an advanceangle addition circuit 220, a start determination circuit 222, and acounter 224. Advance angle range calculation circuit 208 may be referredto as an advance angle range determination circuit, advance angle slopecounter circuit 210 may be referred to as an advance angle slopedetermination circuit, and advance angle initial addition calculationcircuit 212 may be referred to as a multiplier determination circuit.More particularly, FG period counter 202 has an input 202A coupled forreceiving a comparator signal V_(FG) from, for example, comparator 136of FIG. 2 and an output 202B connected to an input 204A of multipliercircuit 204 and to an input 206A of an advance angle storage register206. Multiplier circuit 204 has an output 204B connected to an input216A of subtractor circuit 216.

Advance angle storage register 206 has an output 206B connected to aninput 208A of range determination circuit 208 and to an input 210C ofslope determination circuit 210. Range determination circuit 208 has anoutput 208B connected to an input 210A of slope determination circuit210. In addition, slope determination circuit 210 has an input 210Bcoupled for receiving an advance angle control signal V_(AAL) from anexternal pin 230 and an output 210D connected to an input 212A of amultiplier determination circuit 212, which circuit 212 has an input212B coupled for receiving an advance angle control signal V_(AAH) froman external pin 232. An addition circuit 214 has an input 214A connectedto an output 212C of multiplier determination circuit 212, an input 214Bconnected to an output 220B of an advance angle calculation circuit 220,and an output 214C connected to an input 216B of subtractor circuit 216.Counter 224 has an input 224A coupled for receiving comparator signalV_(FG) and an output 224B connected to an input 222A of startdetermination circuit 222, which circuit 222 has an output 222Bconnected to an input 220A of advance angle calculation circuit 220.

Subtractor circuit 216 has an output 216C connected to an input 218A ofpseudo-FG generation circuit 218, which circuit 218 has an output 218Bconnected to control circuit 12 for transmitting a pseudo-FG signal.

FIG. 4 is a flow diagram 250 illustrating the advance angledetermination in accordance with an embodiment of the present invention.Box 252 represents the start of advance angle processing. Lead angleadjustment circuit 200 operates in a normal advance angle calculationprocessing mode as indicated by box 254. In response to an FG signal atinput 202A, advance angle processing circuit 200 determines whether toadjust the advance angle as indicated by decision diamond 256. Inresponse to control circuit 12 determining that the rotor is notturning, i.e., the NO branch of decision diamond 256 and box 258,control circuit 12 continues operating in a normal processing mode. Inresponse to control circuit 12 determining that the advance angle orlead angle should be adjusted, lead angle adjustment circuit 200determines whether the lead angle of signal VFG equals a target value asindicated by decision diamond 260. If the lead angle matches the targetvalue then advance angle processing is terminated as indicated by theYES branch of decision diamond 260. If the lead angle does not match thetarget value as indicated by the NO branch of decision diamond 260 andbox 262, the lead angle adjustment circuit 200 continues adjusting thelead angle by returning to the process indicated by box 254.

FIG. 5 is flow diagram 270 showing the advance angle calculation processin accordance with an embodiment of the present invention. Lead angleadjustment circuit 200 begins the lead angle count up calculationprocess in response to FG frequency information. The calculation processbegins as indicated by box 272 and the advance angle count up iscalculated as indicated by box 274. Then the advance lead angleadjustment circuit 200 adjusts the lead angle as indicated by box 276.In response to adjusting the lead angle to the desired value, theadvance angle calculation is complete as indicated by box 278.

FIG. 6 is a circuit diagram 300 illustrating a circuit configuration inwhich pins 230 and 232 of lead angle adjustment circuit 200 are coupledfor receiving a ground signal through resistors 302 and 304. It shouldbe noted that pins 230 and 232 are external to the packaging materialthat protect, for example, a semiconductor chip. Resistors serve aspull-down resistors. It should be appreciated that lead angle adjustmentcircuit 200 has been described with reference to FIG. 3. By way ofexample, resistors 302 and 304 are set at values of 47 Kilohms (47 KΩ).

FIG. 7 is a circuit diagram 310 illustrating a circuit configuration inwhich pins 230 and 232 of lead angle adjustment circuit 200 are coupledto voltage divider networks 309 and 313. In accordance with anembodiment, voltage divider network 309 is comprised of resistors 312and 314, where resistor 314 has a terminal coupled for receiving anoperating potential V_(SS) and a terminal connected to a terminal ofresistor 312 at input pin 230. By way of example operating potentialV_(SS) is a ground potential. The other terminal of resistor 312 iscoupled for receiving a control voltage V_(REG). The voltage at inputpin 230 is set in accordance with the values of resistor 312 and 314.For example, the values of resistors 312 and 314 may be 15 kΩ and 47 kΩand the voltage at input pin 230 is approximately 0.75*V_(REG).Similarly, voltage divider network 313 is comprised of resistors 316 and318, where resistor 318 has a terminal coupled for receiving anoperating potential V_(SS) and a terminal connected to a terminal ofresistor 316 at input pin 232. The other terminal of resistor 316 iscoupled for receiving a control voltage V_(REG). The voltage at inputpin 232 is set in accordance with the values of resistors 316 and 318.For example, the values of resistors 316 and 318 may be 47 kΩ and 15 kΩand the voltage at input pin 230 is approximately 0.25*V_(REG).

FIGS. 8 and 9 illustrate plots 320 and 330, respectively, for setting anadvance angle or lead angle in accordance with an embodiment of thepresent invention. Plots 320 and 330 illustrate the voltage at pin 230versus the frequency of the FG signal and the lead angle versusfrequency. It should be noted that the speed of the motor, i.e., therevolutions per minute, can be determined from the FG frequency. Plots320 and 322 may be derived from equation 1 (EQT. 1)Lead Angle=A*fFG+B  EQT.1

where:

-   -   A is derived from pin 232;    -   B is derived from pin 230; and    -   fFG is derived from the frequency of the FG signal.

As discussed with reference to FIG. 5, lead angle adjustment circuit 200counts the number of delta FG signals, i.e., the number times thedifference between an edge of the FG signal and an edge of the drivesignal changes. Briefly referring to FIG. 10, a plot 340 of the FGsignal and the modified FG signal versus time is illustrated. Theportion 344 of plot 340 represents the FG signal and the modified FGsignal. At startup the FG signal has a period that decreases as therotor turns faster. Because of the scales, the FG signal and themodified FG signal appear as a single trace. Thus, the portion withinthe broken lined circle identified by reference character 342 isexpanded so that the FG signal, identified by reference character 346,and the modified FG signal, identified by reference character 348, areseparated out. The modified FG signal may be referred to as an adjustedFG signal or a pseudo FG signal. In this plot, the delta or thedifference in the rising edges of the FG signal and the modified FGsignal identified by the numbers 1, 2, and 3 are increasing with time.The delta or the difference in the rising edges of the FG signal and themodified FG signal identified by number 4 are the same. Thus, lead angleadjustment circuit 200 uses this number as the multiplier A shown inEQT. 1.

FIG. 11 is a plot 350 illustrating the FG signal 352, the modified FGsignal 354, a drive current waveform 356 generated in response to the FGsignal 352, and a drive current waveform 358 generated in response tothe modified FG signal 352. FIG. 11 shows the improvement in the drivesignal in response to the modified FG signal, i.e., drive signal 358does not have the oscillations or the cutoff portions present in drivesignal 356.

Although specific embodiments have been disclosed herein, it is notintended that the invention be limited to the disclosed embodiments.Those skilled in the art will recognize that modifications andvariations can be made without departing from the spirit of theinvention. It is intended that the invention encompass all suchmodifications and variations as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for adjusting a drive signal,comprising: providing a drive circuit, wherein the drive circuitgenerates the drive signal; determining a period of the drive signal;determining a first advance angle and determining a second advanceangle, wherein the first advance angle is a minimum advance angle andthe second advance angle is a maximum advance angle; extracting anadvance angle count value from a storage register in accordance with theperiod of the drive signal; using the advance angle count value and afirst control signal to determine an advance angle adjustment rangewherein the first control signal is from a source external to the drivecircuit; and using the advance angle adjustment range and a secondcontrol signal to determine an advance angle adjustment range startangle wherein the second control signal is from another source externalto the drive circuit.
 2. The method of claim 1, further includingdetermining an angle determination slope using the first advance angleand the second advance angle.
 3. The method of claim 1, furtherincluding generating the drive signal in response to the advance angleadjustment range start angle.
 4. The method of claim 1, furtherincluding terminating advance angle processing in response to the leadangle becoming equal to a target angle value.
 5. The method of claim 1,further including continuing to adjust the lead angle in response to thelead angle not matching a target angle value.
 6. The method of claim 1,further including receiving the first control signal via a first inputand receiving the second control signal via a second input.
 7. A methodfor adjusting a drive signal, providing a drive signal; determining aperiod of the drive signal; determining a first advance angle anddetermining a second advance angle; determining an angle determinationslope using the first advance angle and the second advance angle;extracting an advance angle count value from a storage register inaccordance with the period of the drive signal; one of using the advanceangle count value and a first control signal to determine an advanceangle adjustment range wherein the first control signal is from a sourceexternal to the drive circuit or using an advance angle count range todetermine an advance angle adjustment range wherein the second controlsignal is from one of the source external to the drive circuit oranother source external to the drive circuit; and adjusting the drivesignal in response to the advance angle adjustment range.
 8. The methodof claim 7, wherein the first advance angle is a minimum advance angleand the second advance angle is a maximum advance angle.
 9. The methodof claim 7, further including generating the drive signal in response toa first advance angle adjustment range angle.
 10. The method of claim 7,further including terminating advance angle processing in response tothe lead angle becoming equal to a target angle value.
 11. The method ofclaim 7, further including continuing to adjust the lead angle inresponse to the lead angle not matching a target angle value.
 12. Themethod of claim 7, further including receiving the first control signalat a first input and receiving the second control signal at a secondinput.
 13. A method for adjusting a drive signal, comprising:determining a period of the drive signal; determining a first advanceangle; determining a second advance angle; determining an angledetermination slope using the first advance angle and the second advanceangle; extracting an advance angle count value from a storage registerin accordance with the period of the drive signal; determining anadvance angle adjustment range; and generating a drive signal inresponse to the advance angle adjustment range.
 14. The method of claim13, wherein determining the advance angle adjustment range comprises oneof using the advance angle count value and a first control signal todetermine an advance angle adjustment range or using an advance anglecount range and a second control signal to determine the advance angleadjustment range.
 15. The method of claim 13, further includingterminating advance angle processing in response to the lead anglebecoming equal to a target angle value.